1. Field of the Invention
The present invention relates to an evaporator system for separation of water content in a heavy oil emulsified fuel by way of heating, and an operation method thereof.
2. Description of the Prior Art
As heavy oils of a high consistency nature, in order to make its handling during transportation and storage easier, heavy oil fuel is provided in advance with an appropriate amount of water and surface active agent so as to form what is called a heavy oil emulsified fuel. When this heavy oil emulsified fuel is to be burned in a combustion furnace of a boiler etc., it is desirable to remove water content from the heavy oil emulsified fuel for combustion efficiency.
A prior art evaporator system for separation of water content in the heavy oil emulsified fuel is shown in FIG. 7, and a description will be made thereof. In FIG. 7, numeral 11 designates a tank, in which an emulsified fuel 11a is stored. Numeral 12 designates a pump, numeral 13 designates a preheater, numeral 14 designates an evaporator, numeral 15 designates a separator, numeral 16 designates a heating steam supply equipment and numeral 17 designates a pump.
In the evaporator system of FIG. 7 having such equipment and machinery, the emulsified fuel 11a, containing water, in the tank 11 is fed into the preheater 13 via the pump 12 and a piping 11b. A heat exchanger tube 13a is provided within the preheater 13 for flow of heating water or steam, after separated, as a preheating source medium which is described later, and the emulsified fuel 11a is filled surrounding the heat exchanger tube 13a. 
It is to be noted that the preheating source medium and the emulsified fuel 11a may flow either on the inside or on the outside of the heat exchanger tube 13a. 
The emulsified fuel 11a outside of the heat exchanger tube 13a is preheated to a certain temperature through heat exchange with the preheating source medium and is sent to the evaporator 14 via a piping 13b. Within the evaporator 14 are provided a plurality of generating tubes 14a, 14b, 14c, for flow of the preheated emulsified fuel 11a. 
On the other hand, the emulsified fuel 11a is heated by a heating source medium surrounding the generating tubes 14a, 14b, 14c, the heating source medium being a heating steam, for example, which is supplied from the heating steam supply equipment 16 via a piping 16a, and the heating source medium of which temperature has been lowered is discharged through a piping 16b. Thus, the emulsified fuel 11a within the generating tubes 14a, 14b, 14c is boiled to be evaporated and is then sent to the separator 15 via a piping 14d. 
The emulsified fuel 11a fed into the separator 15 is separated into water content (such as steam) (i.e., water portion) and heavy oil fuel. The water content separated from the emulsified fuel 11a at the separator 15 is sent to the preheater 13 via a piping 15a in a state of heating water or steam to be used as a preheating source which flows in said heat exchanger tube 13a of the preheater 13. After its temperature has been lowered, the water content is discharged out of the system via a piping 15b. 
It is to be noted that a surplus water remaining after the separated water has been taken for said preheating source is extracted outside of the system via an extraction valve 15c and a piping 15d to be used for an atomizing steam etc. Also, the heavy oil fuel of which water content has been separated at the separator 15 is taken out of the system via a piping 15e and a pump 17 to be burned in a combustion system (a boiler, for example) having main equipment, such as a tank, a burner, etc. which are not shown in the figure.
In order to make effective use of the amount of heat input of the heating source medium fed into the evaporator 14, a heat regeneration type is used in which the water content separated from the emulsified fuel at the separator 15 is introduced into the preheater 13 as the preheating source medium so that its heat source is made use of repeatedly, and a design of construction consisting of the preheater 13, the evaporator 14, etc. having a heating area that is compact to the greatest extent possible is employed.
In the prior art evaporator system as described above, it is essential to operate it so as to obtain such a high efficiency water separation so as to bring on a maximum thermal efficiency, a most compact-sized design of equipment and machinery and an always constant predetermined value of water content in the heavy oil emulsified fuel which is obtained after separation.
In the mentioned combustion system (boiler etc.) for burning the separated heavy oil fuel, however, the amount of use of the heavy oil fuel used therein is not always constant but varies unavoidably corroding to load change in the boiler etc. For example, if flow rate of the emulsified fuel is increased from a certain flow rate, because the system is of a closed loop, the amount of the preheating source medium from the piping 15a does not increase rapidly resulting in lowering of outlet temperature of the preheater and change of the operation conditions.
Thus, when the amount of the emulsified fuel (hereinafter called a xe2x80x9cloadxe2x80x9d) sent to the preheater from the tank 11 changes, because the system employs a heat regeneration type, there occurs a delay in delivery and receipt of heat and temperature in each portion changes. Consequently, water content in the emulsified fuel obtained after separation does not become constant, and as one countermeasure therefor, there is given unavoidably a considerable allowance in the design of heating area in the heat exchanger portion of each component of equipment and machinery.
On the other hand, a small amount of light oil content is mixed in the water content separated at the separator 15, and the preheating source medium in which this light oil content is mixed is used for heat exchange at the preheater 13. When this preheating source medium is discharged in a state of steam (gas) from the preheater 13, the light oil content mixed therein in a state of vapor is condensed soon together with the water content so that the oil content is suspended in the water. The oil content once suspended in the water is hardly separated or removed by a general oil content treatment equipment, and draining thereof into rivers and the like becomes impermissible so that there occurs an obstacle in the operation of the evaporator system.
Further, if there occurs a pressure reduction action in the separator 15, the water content in the emulsified fuel which is heated to a high temperature at the evaporator 14 flashes (evaporizes) rapidly and hardly gets out of the surrounding high consistency heavy oil fuel resulting in a state of bubbles in which the emulsified fuel surrounds the steam gas. As the result, the volume of the fuel increases rapidly to fill the separator 15 or to cause an overflow in the water content separation and extraction pipings, separation performance of the water content is deteriorated rapidly, and a large amount of the oil content is discharged out of the system.
In view of the problems as mentioned above in the prior art heavy oil emulsified fuel evaporator system, it is an object of the present invention to provide an operation method of a heavy oil emulsified fuel evaporator system. In this method, a heavy oil emulsified fuel, after being preheated at a preheater, is led into an evaporator to be heated and then to a separator for separation of its water content so as to form a water portion and a heavy oil portion. The water content, after being separated, is used as a preheating source medium for said preheater, and is channeled to the preheater to preheat the emulsified fuel. The water content separation to a predetermined level is enabled irrespective of load change in a heavy oil fuel combustion equipment. The pressure of the preheating medium is regulated so as to be maintained constant.
Also, it is an object of the present invention to provide a heavy oil emulsified fuel evaporator system in which a heavy oil emulsified fuel, after being preheated at a preheater, is led into an evaporator to be heated and then to a separator for separation of its water content. The water content, after being separated, is used as a preheating source medium for said preheater, wherein no light oil content is discharged together with the separated water content.
Further, it is an object of the present invention to provide a heavy oil emulsified fuel evaporator system having a separator into which the heavy oil emulsified fuel heated at the evaporator is led for separation of water content. The separator is able to prevent the water content in the emulsified fuel from flashing therein and being discharged out of the system.
In order to attain said object to enable a predetermined water content separation constantly, the present invention provides an improved operation method of a heavy oil emulsified fuel evaporator system. First, emulsified fuel is preheated in a preheater. The outlet temperature of a preheater or inlet temperature of an evaporator is maintained constant by regulating the temperature of the emulsified fuel. Pressure in a preheating source medium supply piping for leading a preheating source medium into said preheater is maintained constant. The preheated emulsified fuel, is heated in an evaporator, and the temperature difference of an outlet temperature relative to the inlet temperature of the evaporator (evaporator differential pressure) is regulated so as to be maintained constant. The heated emulsified fuel is then separated as discussed above, and the pressure of the preheating medium is regulated.
In case of load change, flow rate of the emulsified fuel flowing into the preheater is increased or decreased, and the temperature, pressure and flow rate at each of the above-mentioned portions change corresponding thereto. However, by employing the above operation control method of the present invention, a rapid change in the inlet temperature and outlet temperature of the evaporator, and the pressure of the preheating source medium in a piping is avoided so as to be suppressed into a slow change. As the result, change in the water content remaining in the heavy oil fuel after being separated of its water content is avoided, and even in the case of load change, the operation to control the water content to a substantially constant and stable level becomes possible in the entire evaporator system as well.
In the evaporator system to which said operation method is applied, it is desirable to employ a buffer portion for storing the emulsified fuel of an increasable amount, as preheated, in the preheater or between the preheater and the evaporator. With this construction wherein the constant temperature emulsified fuel of the increasable amount is stored in advance, even in the case of a load change, the emulsified fuel of a predetermined temperature can be supplied into the inlet of the evaporator, and the water content in the heavy oil fuel separated thereby can be maintained at a predetermined value constantly.
Also, in order to attain said object to discharge no light oil content together with the separated water content, the present invention provides an improved heavy oil emulsified fuel evaporator system. This system comprises a preheater for preheating the heavy oil emulsified fuel of which water content is to be separated. The preheater is constructed of a first heat exchanger using steam as the preheating source medium and having a level switch, and a second heat exchanger communicating with the first exchanger via the flow control valve and using hot water as the preheating source medium so that the heavy oil emulsified fuel to be preheated flows to the first heat exchanger from the second heat exchanger.
The temperature of the preheated emulsified fuel can be regulated by detecting the temperature of the fuel from the preheater, and by controlling the operation of a preheating medium flow control valve. The evaporator differential temperature can be regulated by detecting the temperature of the fuel from the evaporator, and by controlling the operation of a heating steam flow control valve. The preheating medium temperature can be regulated by detecting the pressure of the preheating medium from the separator, controlling the operation of an auxiliary steam flow control valve, and controlling the operation of an extraction steam flow control valve.
According to this evaporator system of the present invention, the preheating source medium is the steam and high temperature hot water in the first preheater, and the high temperature hot water and low temperature hot water in the second preheater. Consequently, evaluation of heat transfer characteristics in the respective preheater becomes facilitated. Thus, by employing a heat exchanger mainly for steam and a heat exchanger mainly for hot water, individual design with a high accuracy becomes possible, and a compact-sized structure and a reduced cost can be attained.
Further, in the system of piping wherein the hot water level in the preheater is detected and controlled, such an operation control as causes a small volume of hot water to flow so that the flow velocity of the preheating source medium in the state of steam does not reach a critical velocity can be done easily. According to such an operation control, a suspended state of the light oil content in the preheating source medium can be avoided, a subsequent oil content removal by a usual oily water separating equipment can be done easily, and drainage into rivers and the like becomes possible.
Also, in order to attain said object to prevent the water content in the emulsified fuel from flashing in the separator and being discharged out of the system, the present invention provides an improved heavy oil fuel emulsified fuel evaporator system. This system comprises a separator into which the heavy oil emulsified fuel flows after being heated, and the separator has a plurality of opening portions in an upward and downward direction in its side wall. A transmitter for transmitting a sound wave and a receiver for receiving said sound wave are provided for said opening portions.
By employing such a separator as so constructed, bubble generation phenomena in the separator can be detected continuously in advance. Therefore, discharge of the heavy oil fuel out of the system due to overflow can be prevented. Also, by a spreading energy of the sound wave, a defoaming effect can be expected.